1. Field of the Invention
The present invention relates to a surface illuminator (i.e. a surface light source, a surface lighting device, a planer or plane light source, a flat light source, an edge light source, a side light source) that uses a plate-like or panel-like light guide (i.e. light guiding member, optical waveguide, optical or light conducting member) and at least one point light source (i.e. a point-like or dot-like light source), such as a light emitting diode/diodes (LED/LEDs).
The present invention further relates to the surface illuminator typically for use in a backlighting or front-lighting of a liquid crystal display (LCD).
2. Description of the Related Art
The liquid crystal displays (LCDs) are being widely used as information displays for mobile or portable electronic information devices such as mobile cellular telephones, digital cameras, video cameras, mobile electronic information terminals such as PDA (private digital assistant), portable or notebook-like personal computers and television receivers.
Since the liquid crystal displays are non-emissive or passive opt-electronic information displays, the liquid crystal displays are generally used in combination with the surface light source as backlighting or front-lighting devices that illuminate the liquid crystal displays from back side or front side thereof.
The liquid crystal display provided with a surface light source having the LED/LEDs with low power consumption and the light guide member (i.e. light guide plate or panel) is being widely used for such mobile or portable electronic information devices, because these mobile electronic information devices are mainly driven by batteries.
A first conventional surface illuminator using a light guide plate and at least one point-like light source is shown as a prior art, for example, in FIG. 5 of U.S. Pat. No.; 6,627,922 B1 (the corresponding Japan Patent publication No.: P2000-315825 A).
According to the specification related to FIG. 5 of U.S. Pat. No.; 6,627,922, the conventional light source is such that: “In the case where such light emitting device is installed on the side surface of the light transmitting plate to constitute a backlight, as shown in FIG. 5, the chip-type light emitting device has a structure constituted in such a manner that a side surface emitting chip-type light emitting device 20 is arranged on one side wall of the light transmitting plate 30 in a definite interval, light is allowed to be incident on the inside of the light transmitting plate 30 and is allowed to be scattered within the light transmitting plate 30 to allow light to be applied from the surface the light transmitting plate 30. As a consequence, a bundle of light that is radiated from one side surface is such that a strong light is emitted in a central direction and the directivity thereof is narrowed down. As a consequence, as shown in FIG. 5, when light emitting devices are arranged in a definite interval on a side surface of the light transmitting plate 30, a portion which is referred to as a dark portion 31 is generated in which light is not allowed to be incident at a portion of the light transmitting plate 30 between the light emitting devices 20. A portion of such dark portion 31 is compensated with light which is reflected and brought back within the light transmitting plate 30, but the dark portion 31 has a problem such that the portion has a different luminance from a portion on which light is directly allowed to be incident so that the luminance does not become uniform on the entire surface of the light transmitting plate 30”.
A second conventional surface illuminator using a light guide plate and at least one point-like light source is illustrated, in which the second conventional surface light source is indicated as a prior art, for example, in FIG. 10 of U.S. Pat. No.; 6,283,602 B1 (the corresponding Japan Patent publication No.: 10-260405).
According to the specification related to FIG. 10 of U.S. Pat. No.; 6,283,602 B1, the conventional light source is such that: “Hitherto, as the foregoing lighting device, the lighting device shown in FIG. 10 is known which has a planar light guide 101 and point-source lights 102 which are positioned to face a light incident surface 101a of the light guide 101. In this conventional device, the light emitted from the point-source lights 102 is diverged by lenses 103, respectively, and the diverged light then radiates in a planar form from a light emitting surface 101b of the light guide 101. In the above known type of lighting device, however, the area in which the light emitted from the point-source lights 102 can be guided is restricted to predetermined angular areas A. A sufficient luminance level of light can be obtained in the areas A, but not in the portions outside the areas A. As a result, the overall light emitting surface 101b cannot emit light with a uniform luminance level.
In these conventional surface illuminators, one or more point-like light sources are positioned adjacent to, in contact with or buried into a side surface of the light guide plate.
These conventional surface illuminators have such drawback that it is difficult to produce a uniform surface brightness or luminance of the light guide plate along entire areas of that surface lighting surface i.e. light output surface, since the point-like light source, especially LED has a very narrow spread angle or directivity and resultantly the surface lighting surface has not only bright areas but also dark areas, i.e. uneven surface brightness or luminance along or over its lighting surface area.
One prior art is U.S. Pat. No.; 6,627,922 B1 (the corresponding Japan Patent publication No.: P2000-315825 A) that discloses a chip-type light emitting diode having a directivity with wide radiation angle in order to improve the drawback of conventional chip-type light emitting diodes having narrow directivity as shown in FIG. 10 of the same U.S. and JAPAN Patent documents. However many number of the improved light emitting diodes (LEDs) are yet required when the LEDs are used in backlighting or front-lighting of the liquid crystal displays with a comparatively large sized viewing screen used as the mobile information terminals.
Another prior arts are disclosed to improve the drawback of the first and second conventional surface light sources or surface illuminator, for example, in FIG. 1 to FIG. 6 of U.S. Pat. No.; 6,283,602 (the corresponding Japan Patent publication No.: 10-260405), in FIG. 1 to FIG. 14 of U.S. Pat. No.; 6,193,383 (the corresponding Japan Patent publication No.: 2000-011723 A), U.S. Pat. No.; 6,283,602 (the corresponding Japan Patent publication No.: 10-284803), Japan Patent publication No.: 10-282368 and U.S. Pat. No.; 5,664,862.
U.S. Pat. No.; 6,283,602 disclosed such a lighting device that in a lighting device in which planar light is emitted from the planar light emitting surface of a light guide by using a point-source light, such as an LED, the emitted light having a uniform luminance level is obtained on the overall light emitting surface. The lighting device has a point-source light 18 for emitting light in a point-like form. A planar light guide 16 radiates light in a planar form from the planar light emitting surface 16a. A linear light guide 19 is disposed between the point-source light 18 and the planar light guide 16. The point-like light emitted from the point-source light 18 is converted into linear light by the linear light guide 19, and the linear light is guided into the planar light guide 16 through the light incident surface 16b. Since the linear light is incident on the planar light guide 16, the light having a uniform luminance level can be obtained on the overall light emitting surface 16a. 
U.S. Pat. No.; 6,193,383 discloses such a linear light source unit that an elongated transparent light leading member is provided above a light source, leading member is provided opposite to the light source and a hole is formed in the light leading member at a position above the light source. The hole has an inverted triangular shape, opposite sides of the hole are provided for reflecting light beams emitted from the light source in a longitudinal direction of the light leading member.
U.S. Pat. No.; 5,664,862 discloses such an edge light for a panel display that the edge light for projecting light into a lighting panel through an end surface of the lighting panel. The edge light includes a thin transparent optical guide member having an elongate portion and at least one end portion extending from the elongate portion. The elongate portion has a planar surface and a shaped surface generally parallel to the planar surface and configured for reflecting light within the guide member through one of the planar surface and the shaped surface. Either the planar surface or the shaped surface is positioned adjacent the end surface of the lighting panel when the edge light is used to illuminate the panel. The edge light also includes a light source positioned at the end portion for projecting light into the elongate portion of the optical guide member.
U.S. Pat. No.; 6,283,602 discloses such linear light guide unit that an elongated transparent light leading member is provided above a light source, leading member is provided opposite to the light source and a hole is formed in the light leading member at a position above the light source. The hole has an inverted triangular shape, opposite sides of the hole are provided for reflecting light beams emitted from the light source in a longitudinal direction of the light leading member.
The surfaces light sources or the linear light guides disclosed in these prior arts are such that the surface illuminator includes a linear (i.e. bar-like or rod-like) light guide member having a linear light output side and dual opposed end surfaces, at least one point light source or LED positioned adjacent to the at least one end surface and a substantially rectangular surface lighting light guiding plate having a side surface and a surface lighting major surface, in which the linear light guide member is positioned adjacent to along the side surface of the surface lighting light guiding plate.
However, the surface illuminators in these prior arts are not yet sufficient to produce a uniform surface brightness or luminance along or over an entire area of a surface lighting or light emitting surface of the surface lighting light guide member.